Sound image localization techniques for localizing a sound image in an arbitrary position differing from an actual sound source using a pair of sound sources (e.g., speakers) have been known in the audio engineering field. To localize a sound image in a target position, the amplitude and phase of an acoustic signal reproduced with a pair of sound sources are adjusted so that the sound pressure difference between the sound pressure arriving at the left ear of the listener from a pair of sound sources and the sound pressure arriving at the right ear of the listener from the pair of sound sources may coincide with the sound pressure difference between the sound pressure arriving at the left ear of the listener from a virtual sound source located in the target position and the sound pressure arriving at the right ear of the listener from the virtual sound source. To derive a control filter for adjusting an acoustic signal, it is necessary to measure a spatial transfer function, which includes a head-related transfer function, from an actual speaker located in a target position to the entrance to the eardrum of the listener.
As a display panel of an image display device, such as a liquid crystal television, is getting larger, a mismatch between a displayed image and a sound begins to develop. For example, when a speaker is arranged in the lower part of the display panel (also referred to as screen), the viewer hears sound coming from the lower part of the display panel even if the announcer is displayed in the middle of the display panel. In the liquid crystal television or the like, it is difficult to arrange a speaker behind the display panel as in a movie theater.
To overcome the difficulty, the application of sound image localization to such a large image display device may be considered. However, since the head-related transfer function varies widely according to a direction in which a sound comes from the sound source, it is difficult to construct a method of identifying a head-related transfer function when sound image localization is applied to an image display device whose speaker arrangement differs according to the model, screen size, or the like.
Therefore, in the sound image localization apparatus, it is necessary to derive a control filter easily.